This invention relates to a RMS transducer for use in a rapidly responsive voltage regulating system, and more particularly, to a voltage regulating system for an AC power system.
The term RMS, or root-mean-square, is widely employed in the electrical arts. In a time varying or alternating current (AC) waveform, the RMS is a value which may be used for an accurate computation of power. In many AC voltage regulating systems, the RMS voltage at a critical point in the AC power system in monitored. When the monitored RMS voltage at the critical point sufficiently departs from a prescribed value, means are activated for causing it to return to its prescribed value. Such means may include voltage regulating systems employing reactive compensation means such as that disclosed in U.S. Pat. Nos. 3,936,727 and 3,468,432, respectively issued to Kelley et al. and Kelly, on Feb. 3, 1976 and July 6, 1976. These patents are assigned to the assignee of the present invention and are hereby incorporated by reference in the present application.
The Kelley et al., Kelley system disclosed in the previously mentioned patents is suitable for use in industrial power systems serving an erratic reactive load, e.g., an arc furnace, as well as in electrical utility transmission systems for regulating voltage. In very brief terms, the Kelley et al., Kelley system provides input signals for rapid static switching of a reactive converter which can controllably supply compensating leading or lagging current or VARs. The reactive converter comprises fixed inductor means and fixed capacitor means. Static switching means are disposed in series circuit relation with the fixed inductor means. The static switching means includes gating means for controlling the conduction angle of the switching means. In the transmission system application, the RMS voltage at the critical point in the AC power system at which good voltage regulation is desired is compared with a desired RMS value. A sufficient difference therebetween produces an output signal which is utilized for adjusting the conduction angles of the inductor means of the reactive converter. More particularly, if the monitored RMS value at the critical point is sufficiently below the prescribed value, a signal is generated which causes the reactive converter to provide leading current or VARs into the system. This has the effect of raising the system RMS value of the voltage to the prescribed value. Conversely, if the monitored RMS voltage at the critical point is sufficiently above the prescribed value, a signal is generated which causes the reactive converter to provide lagging current (VARs) or less leading current (VARs) so as to have the effect of lowering the system RMS voltage value to the prescribed value.
In the previously described Kelley et al., Kelley system, the reactive converter rapidly responds to adjust leading and lagging current (VARs) each one half cycle. However, the responsiveness of a voltage regulating system employing such a reactive converter is limited by the time delay in monitoring the RMS voltage at the critical point in the power system at which good voltage regulation is desired. In this connection, known RMS transducer means are generally of three types: thermalmeters; diode arrangements employing logarithmic functions and filters; and operational amplifiers employing filters. These RMS transducers provide undesirable time delays in monitoring the RMS value so as to be generally undesirable in a voltage regulating system of the type employing the previously described Kelley et al., Kelley reactive converter.
Therefore, it is a general object of this invention to provide rapidly responsive means for determining the RMS value of a time varying waveform.
Another object of this invention is to provide transducer means which is updated each one half cycle.
Another object of this invention is to provide such transducer means which is substantially unaffected by harmonics.
Another object of this invention is to provide such transducer means which is substantially unaffected by both odd and even harmonics.
Another object of this invention is to provide a rapidly responsive voltage regulating system for an AC power system employing RMS voltage transducer means.
Another object of this invention is to provide such a voltage regulating system in which the transducer means is capable of determining the RMS value of the last cycle in the voltage waveform.